Spectrometry is a well-known technique used to identify the characteristics of gas, liquid, and solid samples, wherein light is directed at a sample and the light reflected from or transmitted through the sample is then analyzed for changes in wavelength. These changes provide information regarding the composition of the sample, its chemical bonds, and other features. Many spectrometers have a sample chamber which is located in a fixed location, with emitted light being directed into the chamber and exiting light being collected by an adjacent detector. However, such an arrangement can be inconvenient owing to the need to load the sample chamber prior to analysis of the sample, and thus spectrometers have been developed which allow “remote” sampling: a mobile probe is provided which can be situated within or adjacent to a sample of interest, with the probe emitting and collecting the light for analysis. Such an arrangement is exemplified by the SABIR probe provided with the ANTARIS spectrometer (Thermo Electron LLC, Madison, Wis., USA), which is schematically illustrated in the simplified diagram of FIG. 1. A spectrometer 100 includes an interferometer 102 emitting light at some specified wavelength(s), and this light is received by a fiberoptic cable 104 and transmitted to a gun-like probe 106, at which the light is emitted from an emission location 108 at the tip of the probe 106 onto a sample. The light is then picked up at a collection location 110 after being diffusely reflected from the sample (i.e., the light penetrates the sample to some degree before being reflected outwardly), and is transmitted back to the spectrometer 100 via a return fiberoptic cable 112 to be received at a photosensitive detector 114. The readings from the detector 114 are then processed to provide information regarding the properties of the sample. This diffuse reflectance mode of measurement is commonly used for solid samples, which tend to exhibit higher degrees of diffuse reflectance.
However, measurements of diffusely reflected (scattered) light from a sample may sometimes be weak, which can lead to difficulties in accurate sample analysis. It may then be desirable to measure light transmitted through the sample. In this case, a mirror may be situated within the sample, or on a side of the sample opposite the probe 106, so that the light from the emission location 108 passes through the sample, is reflected back through the sample from the mirror, and is then picked up at the collection location 110. This mode of measurement, known as transflectance, is commonly used for liquid and gas samples which exhibit low diffuse reflectance. Another mode of measurement, known as transmittance, modifies the probe 106 so that the collection location 110 is located opposite the emission location 108 with a space therebetween into which the sample may be received. The light then passes through the sample directly from the emission location 108 to the collection location 110.
In some cases, it may be desirable to analyze a sample using more than one of the foregoing reflectance, transmittance, and/or transflectance modes. This generally requires that the probe 106 be reconfigured or replaced so that the desired modes may be sequentially implemented on the sample, and such reconfiguration/replacement can be time-consuming and inconvenient.